Numerous fitting mechanisms have been developed for coupling a pair of pipe members. For instance, U.S. Pat. No. 2,270,296 relates to a pipe coupling unit having a flange radially extending from and permanently secured to an end of a pipe section for attaching the pipe section to an adjacent pipe section, while U.S. Pat. No. 3,752,509 relates to a sealed joint having a metal-to-metal seal for connected tubes.
A unique problem is presented when a pipe element is coupled to another pipe element through an opening formed in a curved wall having a non-uniform thickness resulting from a manufacturing process, such as a blow molding process. Because of the non-uniform thickness of the wall, it is especially difficult to couple the pipe elements in a desired orientation. For instance, FIGS. 1A and 1B show an adapter A fixedly attached to an elbow pipe B, which is mounted within a housing C (only a portion which is shown in FIGS. 1A and 1B) of a filter. The adaptor A is provided with a radial flange E fixedly formed thereon at an end thereof. An opposite end (not show) of the elbow pipe B is fixedly attached to another part of the filter (not shown), such as a diffuser. An opening F, which is formed in a curved wall G of the housing C having a non-uniform thickness, provides an access for coupling the adapter A to an external pipe (not shown) via a bulkhead fitting H. Partly due to the non-uniform wall thickness, the opening F has a non-uniform depth around its periphery. More particularly, the depth of a top portion of the opening F (indicated by double-headed arrow D.sub.1 in FIG. 1A) is greater than the depth of a bottom portion of the opening (indicated by double-headed arrow D.sub.2 in FIG. 1A). Because the flange E is immovable relative to the elbow pipe B, as the adapter A is assembled with the wall G by threading the bulkhead fitting H to the adapter A through the opening F, an axial thrust created by the threading action between the adapter A and the bulkhead fitting H directly acts on the adapter A and thereby continuously aligns the adapter A and the elbow pipe B. Thus, after the assembly (see FIG. 1B), the adapter A is aligned in an orientation in which both top and bottom portions I, J of the flange E bear against portions K, L, respectively, of the curved wall G. As a result, the longitudinal axis of the adapter A after the assembly (indicated by alternating sequence M of a pair of short lines and a long line in FIG. 1B) is out of alignment with the pre-assembly orientation of the longitudinal axis (indicated by alternating sequence N of a pair of short lines and a long line in FIG. 1B). Such misalignment of the longitudinal axis of the elbow pipe B is undesirable because the connection at which the opposite end of the elbow pipe B is fixedly attached to a part of the filter is subjected to a stress by the force creating the misalignment. In addition, due to this misalignment, a gap O is formed between the bulkhead fitting H and the wall G (see FIG. 1B), and, as a result, the bulkhead fitting H provides an insufficient fluid seal.
While numerous prior art devices for coupling a pair of pipe elements have been developed, they do not specifically address this problem. Accordingly, there is a need for a coupling device addressing this problem.